1. Field of the Invention
This invention is directed to a process for selectively producing ethanol which comprises introducing into a reaction zone (1) methanol, (2) hydrogen, (3) carbon monoxide, (4) a cobalt tricarbonyl complex, (5) an iodine compound and (6) a ruthenium compound and then subjecting the contents of said reaction zone to an elevated temperature and an elevated pressure for a time sufficient to convert methanol to ethanol.
2. Description of the Prior Art
Ethanol is a compound which has been used by man since time immemorial. Historically, ethanol has been produced for various purposes by the fermentation of common grains. However, within recent years synthetic processes have been developed to synthesize this alcohol for industrial use. Such synthetic processes permit the use of more economical starting materials than those used in the fermentation processes, and, additionally, permit production and reproduction of a more standardized product and more easily predictable yields of end product. Methanol can easily and economically be produced in great quantities from hydrogen and carbon monoxide or from almost anything containing carbon and hydrogen, for example, from methane to manure and from coal to crude oil residues. One such process for producing ethanol synthetically involves reacting methanol with carbon monoxide and hydrogen at elevated temperatures and pressures in the presence of a catalyst system.
The conversion of an alcohol, for example, methanol, to the primary alcohol containing one carbon atom more than the original alcohol, namely ethanol, is normally a tedious and time-consuming procedure involving a series of steps. Additionally, catalysts which possess acceptable activity generally tend to give a wide spectrum of products in addition to ethanol, for example, hydrocarbons and oxygenated hydrocarbons having a broad distribution of carbon atoms. This not only complicates the separation and recovery of desired products, but results in reduced yield of ethanol and erosion of reactants in the production of undesirable by-products.
The reaction of methanol with hydrogen and carbon monoxide to produce ethanol is appreciated and disclosed by the prior art. However, in general, most known processes produce an undesirably large mixture of alcohols, aldehydes, ketones and carboxylic acids in addition to the desired alcohol.
For example, U.S. Pat. No. 4,013,700, entitled "Catalytic Process for Polyhydric Alcohols and Derivatives," issued to Cawse on Mar. 22, 1977, discloses a process for the preparation of polyhydric alcohols, their ether and ester derivatives, and oligomers of such alcohols. In particular, these alcohols and their derivatives are produced by reacting the oxides of carbon and hydrogen in the presence of a quaternary phosphonium cation and a rhodium carbonyl complex at elevated temperature and pressure.
Another process is set forth in U.S. Pat. No. 3,248,432, entitled "Process for the Production of Ethyl Alcohol," issued to Riley et al, on Apr. 26, 1966, which relates to a process for the production of ethyl alcohol by the interaction of methanol, carbon monoxide and hydrogen. In particular, these compounds are reacted at elevated temperature and pressure in the presence of a cobalt catalyst and an iodine promoter. Examples of suitable cobalt sources are described as any water-soluble source of cobalt, for example, the cobalt carbonyls, the lower salts of alkanoate cobalt, such as cobalt acetate, cobalt formate, cobalt propionate, and the like.
U.S. Pat. No. 2,623,906, entitled "Preparation of Organic Hydroxy-Containing Compounds by Reacting Alcohols With Carbon Monoxide and Hydrogen," issued to Greshaw on June 16, 1948, relates to a procedure for synthesizing mono and poly functional oxygen-containing organic compounds by the reaction of alcohols, carbon monoxide and hydrogen. Catalysts described as suitable for use include various cobalt compounds, for example, cobalt carbonyl, cobalt carbonyl hydride, metallic cobalt, and organic and inorganic cobalt salts. The process, however, suffers from the disadvantage of poor product distribution.
U.S. Pat. No. 3,285,948, entitled "Halides of Ruthenium and Osmium In Conjunction With Cobalt and Iodine in the Production of Ethanol From Methanol", issued to Butter on Nov. 15, 1966, teaches a method for producing alcohols in which any source of cobalt soluble in the reaction medium which will yield a cobalt carbonyl or hydrogen cobalt carbonyl under the reaction conditions can be used. In addition, an iodine promoter is employed, for example, iodine or alkali metal iodines. A secondary promoter is also employed, i.e., ruthenium halide or osmium halide. High selectivity is described as better when the secondary promoter is used in combination with the primary promoter and other reactants.
Dutch Pat. No. 760.6138, entitled "Process for the Formation of Ethanol from Methanol and Synthesis Gas," issued to Shell International Research on June 8, 1976, relates to a process for producing alcohols which utilizes any soluble cobalt source which can generate a cobalt carbonyl or hydro carbonyl by reaction with synthesis gas. For example, sources of cobalt suitable for use are cobalt iodide or cobalt metal from which ions can be generated in situ. Organic salts of cobalt such as cobalt acetate, formate, or propionate are described as especially good sources; an iodide or bromide promoter is also utilized. In addition, the use of a tertiary phosphine is described as affording improved selectivity to the formation of alcohols.